One prior art apparatus is a reverberatory type furnace which simply passes the combustion heat through, or over the top of the solid metal charge material before exiting a flue in the roof. This apparatus makes very minimum use of the combustion energy. This apparatus also directs the combustion flame at an internal refractory wall. This apparatus is not wholly satisfactory, however, because it requires the furnace melting chamber be completely shut down to repair or service any damage done to the internal walls by the combustion flame. Additionally this apparatus makes no provision to allow for the holding or storage of more than one molten metal alloy. The entire molten metal bath must be drained and the walls and floor cleaned, to prevent metallurgical contamination, before filling with a different molten metal alloy.
Another type of prior art apparatus is a non-crucible refractory lined furnace that uses a vertical shaft, or stack in which to place solid metal charge material. Combustion energy is applied at the base of the vertical shaft and causes the metal to melt as the heat passes up through the metal charge to exit a flue in the roof. This apparatus requires the solid metal charge material be placed in the top of the furnace and does not allow for placing large stacks of ingot, or sows on the floor of the furnace with a forklift, or other mechanized device. This apparatus also directs the combustion flame at an internal refractory wall. This is not wholly satisfactory, however, because it requires the furnace melting chamber be completely shut down to repair or service any damage done to the internal walls by the combustion flame. Additionally this apparatus makes no provision to allow for the holding or storage of more than one molten metal alloy. The entire molten metal bath must be drained and the walls and floor cleaned, to prevent metallurgical contamination, before filling with a different molten metal alloy.